Embodiments in accordance with the present invention relate to a track allocation method of a disk drive. Particular embodiments in accordance with the present invention relate to a method of allocating a track group to a disk drive wherein there exist a plurality of track widths in a zone which is a group of tracks each having the same number of sectors.
As a method to improve recording density of a disk drive, its track width and track density are shortened. One of the ways of achieving this is to make a writing head and a reading head of the disk drive finer. By making the head finer, it becomes possible to write data to a track with narrower width. Further, the track density is improved by shortening the track width. The writing head and the reading head are fixed to an arm, and the arm is driven by a voice coil motor. Since the arm is moved by the voice coil motor, an error is caused as the arm moves. Therefore, there is possibility that the writing head juts out into the tracks on both sides of the subject track and destroys data. In order to prevent such data destruction, a track pitch is made to be larger than the track width to secure a writing margin. About 10 percent of the track width is provided on both sides of each track as a writing margin, which obstructs the improvement of the track density. The writing margins are needed on both sides of each track on the disk drive to write data to sectors at random. However, deletion of one of the writing margins becomes possible when writing data in sequence. Therefore, the improvement of the track density becomes possible that much. In other words, the capacity of the disk drive can be improved by about 10 percent even when using the same writing head, reading head, and storage medium.
The track pitch cannot be made narrower than the width of the writing head in the conventional method of writing data for the disk drive. Therefore, the smallest track pitch is determined by the width of the writing head. Accordingly, the method of reducing the track width to be less than the width of the writing head is needed to improve the capacity of the disk drive more than the amount of deletion of the writing margin. As such a method, the track width is enabled to be smaller than the width of the writing head by partially overwriting the adjacent tracks in U.S. Pat. No. 6,185,063 and WO99/45534.
In addition, U.S. Pat. No. 6,185,063 proposes two methods, namely, “write seldom format” and “paired format,” as methods of overwriting tracks partially. The rate of reducing the track width is improved if a given track is made unable to be overwritten in a given order in the “write seldom format” by partially overwriting a plurality of tracks mutually. On the other hand, in the “paired format,” the rate of reducing the track width decreases if a given track is made unable to be overwritten in a given order by partially overwriting two adjacent tracks.
In the case of saving data like video and audio data of which main purpose is referencing, since contents of the file storing video and audio data are hardly necessary to be updated, they are saved on the “write seldom format” track. On the other hand, since updating takes place in meta information, which is management information of a file, simply by reading the file. Therefore, it is effective to save it on the track of the “paired format.”
Further, WO99/45534 proposes a disk drive wherein a zone comprising tracks each having the same number of sectors is divided into a plurality of areas whose track pitches are different.
Deletion of one of the writing margins of the track means that the track is limited to be written in one direction. This also means that it is necessary to divide an area on a storage medium into a plurality of areas and rewrite those areas collectively. Namely, when troubles such as a power failure and a runaway of a host take place and the writing processing is interrupted, there is possibility of destroying data of the track to be written to next because the writing margin doesn't exist. In the “magnetic disk drive” described in WO99/45534, due to its structure wherein adjacent tracks are partially overwritten, the data overwritten are lost.
To prevent such data destruction, WO99/45534 proposes to write additionally for each track or sector and to manage the relation between a logical block address (Logical Block Address, LBA) and a physical block address (Physical Block Address, PBA) by an address translation table. In this method, however, there is a problem of the address translation table becoming huge in volume. For example, when address translation of each sector on a disk drive with capacity of 100 GB is managed, the width of 28 bits is needed in LBA since there are 200 M numbers of sectors and one entry of the address translation table becomes 56 bits. Thus, the size of the address translation table becomes 1.4 GB. Since such a huge address translation table will be stored on the storage medium of the disk drive, the capacity of the disk drive is reduced. Further, since it takes time to search the address translation table, the performance of the disk drive is also lowered.
In order to avoid the performance degradation of the disk drive when updating data, it is effective for a high-order device to update collectively not a sector or a track but a plurality of tracks of which adjacent tracks are partially overwritten. It is desirable that sizes of subject data are the same capacity for the high-order device to update data collectively. There is a technique to allow such data updating wherein the same numbers of tracks are grouped in a zone and regarded as a unit of data update, and wherein the number of tracks in the zone is made to be an integral multiple of the number of tracks of the data update unit.
On the storage medium, there exist defective sectors where data cannot be read out due to the defects made when the storage medium is manufactured and the aged deterioration. Since defective sectors are generated stochastically, the servo data containing positioning information of a head might become a defective sector. The servo data are recorded in a plurality of places on the same track. When some of such servo data are defective sectors, the entire track is assumed to be a defective track and its use is prohibited. Therefore, if the number of tracks in the zone is an integral multiple of the number of tracks to be a data update unit, the track group whose number of tracks doesn't reach the number of tracks of the data update unit cannot be used even when only one defective track is generated. In order to cope with such a problem, there is a method wherein a spare track is prepared in the zone and a defective track is replaced with the spare track. Since it is not possible to predict how many defective tracks are generated, more spare tracks than actually required may be prepared. Because the effective capacity decreases as much as the amount of unused spare tracks, the effect of partially overwriting the adjacent tracks and increasing the capacity is lowered.
WO99/45534 proposes a disk drive wherein a track group with a plurality of track pitches exists in a zone. However, it doesn't disclose a method of allocating tracks to solve the above-described problem.